It is widely known in the art that the electromagnetic pilot type selector valve of this type is divided to a single-solenoid type selector valve having a pilot valve unit provided with a single solenoid mechanism and a double-solenoid type selector valve having two solenoid mechanisms.
In general, the double-solenoid type selector valve comprises a main valve unit having a spool type main valve disc to switch over main fluid, and a pilot valve unit provided with two solenoid mechanisms for switching pilot fluid. By actuating these solenoid mechanisms alternately, pilot fluid is switched over, and by alternately applying pilot fluid pressure on pistons on both ends in axial direction of the main valve disc, the main valve disc is switched over.
The single-solenoid type selector valve comprises a main valve unit having a spool type main valve disc for switching main fluid, and a pilot valve unit provided with a solenoid mechanism for switching pilot fluid. The main valve disc is pushed permanently in one direction at one end in axial direction by force of a spring or by pilot fluid pressure, and by turning on or off the solenoid mechanism to apply or release pilot fluid pressure to the piston on the other end of the main valve disc, the main valve disc is switched over.
The double-solenoid type selector valve and the single-solenoid type selector valve are generally constituted by special-purpose components, and it is practically impossible to use the components in common for these two types of valve except a few parts.
However, it is desirable to use common components for these two types of valves. For example, if it is designed in such manner that a double-solenoid type selector valve is produced by assembling two solenoid mechanism on a valve body assembly and that a single-solenoid type selector valve is produced by assembling a solenoid mechanism on the same valve body assembly, it will be very convenient for manufacture, parts control and maintenance as well as for repair when in trouble or change of models of the electromagnetic valve. Further, it will be possible to reduce the costs.